Water heaters for use in the home, apartments, or other relatively small building units having comparable demands for heated water often employ natural gas as the source of heat. Such water heaters usually comprise a cylindrical body including a tank for storage of water to be heated, a cold water inlet, a hot water outlet, and an apparatus for applying heat to the stored water including a natural gas inlet, control valves and associated thermostat mechanisms, and a combustion chamber in which the natural gas is burned and which is adapted to conduct or otherwise convey the heat of combustion to the quantity of stored water.
The lower region of the cylindrical body includes a combustion air inlet opening communicating the combustion chamber with the room air. A vertical flue pipe extends from the combustion chamber through the tank to an open end at the top of the water heater body. A draft hood is provided at the top of the water heater body to make a connection between the open end of the flue pipe and a conduit leading to a chimney or other existing passage to a roof top opening. The draft hood is generally conical, with a wider lower end mounted on brackets in a position raised above the top of the water heater and concentric with the top end of the flue pipe. The narrower upper end of the draft hood is sealed to the chimney conduit. The draft hood thus reaches down from the chimney conduit as a skirt around the end of the flue pipe to define an open annular space therebetween.
Operation of the water heater is usually vented by the force of convection currents caused by the the heat of combustion. Room air is drawn into the combustion chamber through the combustion air inlet opening, and flue gases rise out of the combustion chamber through the flue pipe to the chimney connection. Convective flow of the flue gases out through the chimney is aided by a draft of room air entering the chimney conduit directly through the open skirt arrangement of the draft hood.
Such conventional water heaters have several disadvantages. A particular disadvantage is caused by the use of room air as combustion air for the water. Energy expended to heat, cool, or humidify room air is wasted when that air is drawn into the water heater and driven out through the chimney. Room air continues to exit through the chimney when the heater rests between intermittent heating operations since the heat contained in the tank of water tends to induce a residual convective flow through the heater. In addition to wasting the energy of heating or air conditioning, this continued loss of room air carries with it the heat stored in the tank of water. Furthermore, an outward draft of room air tends to induce an inward draft of outdoor air through door and window frame spaces, which is undesirable in both winter and summer.
Another cause of loss of room air is the open arrangement of the draft hood as a skirt around the top end of the flue pipe. This opening allows a flow of air from the interior of a house out through the chimney.
Another disadvantage is that conventional water heaters can be installed only in locations where a chimney connection can be made. Construction of a chimney to accommodate a water heater in an existing building is likely to be impractical if not impossible and installation in a building which does have a chimney is limited to locations adjacent the chimney which may not be practical for plumbing and/or electrical requirements. It also may not be desirable to design the location and clearance around a chimney in a new building, particularly a home, to accommodate placement of a water heater.
Known domestic type indoor water heaters and associated venting systems thus fail to provide a means for heating water without wasting valuable energy used to heat or otherwise condition indoor room air, and are not readily adaptable to installation in convenient locations in new or existing building structures.